It is known in the art to control an electric machine by a frequency converter consisting of a plural number of supply and inverter units connected to a common direct voltage intermediate circuit. Some of the units may be provided with a separate unit-specific control, while others, inverter units for example, may be controlled by a common control. The common control in question may be implemented, for example, by branching the control of one control unit to a plurality of inverter units with a separate branching unit.
Parallelism may also appear in other features of an electric drive system. For example, an electric machine may have a plurality of windings galvanically separated from one another, where each winding of the electric machine is controlled by a separate inverter unit. Likewise, a supply may consist of a plurality of supply transformers or a supply transformer provided with a plurality of secondary windings.
However, in the above arrangements, a malfunction in one of the system units may bring the entire system into a halt.